The present invention relates generally to joining sheet metal or other sheet materials and more particularly to an apparatus for forming such joints which are leakproof and have an enhanced mechanical interlock.
It is old in the art to join a plurality of pieces of sheet metal by punching or otherwise manipulating them to cause them to be deformed into an interlocking relationship in a localized area. However, insofar as Applicant is aware, many such joints typically require the shearing of the sheet material and hence are not suitable for leakproof applications unless a sealant is applied. The formation of such joints is also frequently destructive of the corrosion resistance of coated materials. In addition, the known apparatuses for forming the joints are frequently relatively complex in design, often requiring powered actuation of both a punch and one or more portions of the die, and frequently require expensive and complicated sliding die portions. This complexity increases the cost of the equipment, as well as the energy required for operation.
It has therefore been a primary object of the inventions of Applicant's aforesaid prior applications for patents to provide an improved method and apparatus for permanently joining sheet metal or other sheet material items with the capability of forming either leakproof joints or partially "lanced" joints. Additional objects resided in the provision of such a forming apparatus that is relatively simple but durable in construction, that can utilize standard or specialized punches, that requires very little power, that is compact and hence usable in many different applications, that substantially preserves the corrosion resistance of coated sheet materials being joined, and that is suited for use either as part of a small press or in C-frame holders in larger presses. Other objects resided in the provision of an improved die assembly for use in sheet material joining apparatuses, and which is readily adapted to many different joint configurations, including conventional or partially "lanced" joints as well as a novel leakproof joint.
A number of versions of Applicant's joining techniques have been disclosed and/or patented in the aforesaid patents and applications for patent, including one which has as its object the provision of a further improvement in which leakproof joints can be formed which have the visual appearance of rivets, and which therefore can be used in decorative highly visible applications, such as on the outside sides of a vehicular bus or other vehicles, or on the outside surfaces of appliances, or similar applications. Because this is accomplished using the same general principles of operation as Applicant's aforesaid prior inventions, such improvement also meets many of the objects of the prior inventions.
Although Applicant's prior developments discussed above have performed well and have represented significant strides forward in the art, thus enjoying considerable commercial success and acceptance in the industry, the present invention seeks to further enhance the mechanical interlock and joint strength, including the resistance to shearing and peeling forces exerted on the joint. In accordance with the present invention, this enhancement of the joint is accomplished by forcibly flattening the first stage of the joint, which is preferably substantially the same as the joint formations of Applicant's prior developments, thereby forming a second stage joint with such enhanced characteristics. In a preferred form of the invention, such flattening to form the second stage joint is accomplished by placing the formed first stage joint between a pair of anvils that are forcibly movable longitudinally relatively toward one another in order to flatten the first stage joint therebetween. These secondary anvils can both be separate from the anvil typically used in the forming of the first stage joint, or one of the secondary anvils can be the same as the anvil used in forming the first stage joint.
These and other objects, features and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.